The invention relates to magnetometers and, more specifically, comprises a microelectromechanical (MEMS)-based magnetostrictive magnetometer based on the deflection of a Terfenol-D coated single-crystal silicon cantilever for measuring a dc magnetic field with a sensitivity near 1 .mu.T.
Interest is increasing in the development of miniature magnetometers for mapping magnetic fields in extraterrestrial, industrial, biomedical, oceanographic, and environmental applications. The many potential uses of such instruments include the following:
Space physics--for the measurement of absolute field levels and curl of interplanetary space (using suitable arrays of sensors) and satellite-generated fields. PA1 Oceanography--for the detection of ships, mineral deposits, and other magnetic objects. PA1 Biomedicine--for the imaging of magnetic patterns, and, for example, tracking the location and orientation of instruments in microsurgery (the latter will be particularly helpful as the technology moves more to robotic or tele-operated systems). PA1 Environmental science--for the imaging or detection of magnetic fields on the earth's surface or in the atmosphere, for example, in the detection of pipeline corrosion. PA1 Transportation--for the measurement of deflections in crash test experiments and as one of the many sensors in automatically piloted road vehicles.
The trend in magnetometer design and development is constantly toward smaller size, lower power consumption, and lower cost for similar performance. To meet these objectives, recent innovations have included the use of piezoresistive cantilevers and magnetometers based on electron-tunneling effects.
A reported piezoresistive device consists of a single-crystal silicon cantilever, 200 mm long, onto the end of which is glued a small (700 ng) grain of magnetic material. Measurements performed either at low temperature (59.1 K) with a microcrystal of a high-critical-temperature superconductor or at room temperature with a small iron crystal gave sensitivities of 5 and 50 mT, respectively.
A magnetometer based on electron tunneling is bulk-micromachined from silicon. It consists of a silicon substrate on which a fixed electron tunneling tip is etched and a deflection electrode is deposited, and is bonded to a low-stress silicon nitride membrane (2.5.times.2.5 mm). The deflection of the membrane is caused by the Lorentz force induced between the applied fields and the current flowing in a multiloop conductor deposited on top of the membrane. To date, it has been possible to produce only a single loop, resulting in a preliminary noise equivalent magnetic field of only 6 .mu.T.sqroot.Hz.
As can be seen, the sensitivities of the above magnetometers, defined as the minimum detectable field change, are generally in the range of 1 .mu.T to 1 mT, corresponding to 10.sup.-2 to 10 Oe. There is still the need, then, for small, low-cost, low-power-consumption magnetometers with sensitivities capable of meeting the potential applications discussed above.